Im design a power supply to work with heating wires and one of the task is to estimate the temperature of the bare wire for a given current or power consumption.

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I've tried to measure the temperature with a k type thermocouple but the measurement itself affects quite a lot the temperature of the wire in the contact point so I get a lower temperature value.

I've also made measurements of voltage and current on the wire and I don't expect of that measurements to have significant errors so I actually have a reasonable idea of the variation of resistance value.

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Even though the X axes (temperature measurements) are wrong, is it reasonble to use the change in the resistance value to stimate the temperature of the wire by using the temperature coefficient of each wire?


Those are the wires I'm working with

Ferronikel 0.3mm:

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Khantal (most likely) 0.3mm:

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Nichrome 0.1mm:

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This is the variation of resistance measured for the wires, nichrome is 1/3 of the diameter of the other two so it's resistance it's significantly bigger:

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And this is a plot of T vs delta_R using the linear model

R_t = R20(1 + alpha*delta_t)

According to this nichrome and kanthal are around 1000 degrees while the ferronickel wire is more close to the 600 degrees

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I've also found a table that relates color with temperature

The table is consistent in the with the experimental data in the aspect that nichrome and kanthal wires have reached higher temperatures but it's hard to me to choose or to guess which color does have each wire

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I would say:

Ferronikel -> bright cherry -> 790
kanthal -> orange -> 940
Ferronikel -> orange -> 940

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    $\begingroup$ You might find the data in Kaye and Laby of use? kayelaby.npl.co.uk/general_physics/2_6/2_6_2.html $\endgroup$ – Farcher May 10 '16 at 8:36
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    $\begingroup$ That's a common technique to measure the temperature of heated wires, but you have to use a four point measurement. Do you now about that technique? $\endgroup$ – CuriousOne May 10 '16 at 8:38
  • $\begingroup$ @CuriousOne Yes, I know it, I did it that way but if you could link me any paper related with the use of the technique that would be great. I've only found technical sheets like this one: tek.com/sites/tek.com/files/media/document/resources/… My tutor doesn't like I make reference from those sheets. $\endgroup$ – Luis Ramon Ramirez Rodriguez May 10 '16 at 8:55
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    $\begingroup$ You are basically doing it all the right way, already. I have never seen a paper on the subject... it's such an obvious technique and has probably been done for a century or longer that it really doesn't need much of a theoretical backing. If you are worried about the temperature calibration, then you could use an IR thermometer and put a wire coil into a reflective metal can to get a nice black body spectrum without too much effort. $\endgroup$ – CuriousOne May 10 '16 at 9:03
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    $\begingroup$ At some point I would assume you are going to use the heater to, well, heat something. Often the concern isn't the temperature of the heater wire, but instead the temperature of the object being heated. Focus on using a measurement of the object, and control the heater that way. $\endgroup$ – Jon Custer May 10 '16 at 14:26

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